1. Field
Example embodiments relate to variable bit rate video coding. Also, example embodiments relate to methods and apparatuses for controlling bit rates in variable bit rate video coding by setting a quantization parameter of each frame using a measure calculated for each frame.
2. Description of Related Art
Generally, video compressing (or coding) techniques use constant bit rate (CBR) coding methods or variable bit rate (VBR) coding methods. The constant bit rate coding method encodes a video signal, such as a broadcast signal, into a predetermined number of bits for a predetermined period of time. The constant bit rate coding method allocates the same number of bits to both a still image and a moving image. Thus, the quality of the moving image is poor in the constant bit rate coding method because the moving image requires a larger number of bits allocated thereto.
The variable bit rate coding method allocates bits to a video signal in response to the characteristic of the video signal (for example, in response to whether the video signal corresponds to a still image or a moving image) when there is a sufficient bandwidth or when a storage medium such as a digital video disk (DVD) is used. The variable bit rate coding method may allocate a larger number of bits to a moving image so that it can improve the quality of the moving image as compared to the constant bit rate coding method. Accordingly, the variable bit rate coding method is used for Moving Picture Experts Group (MPEG)-4 and H.264, which are applied to next-generation DVD recorders, as well as for MPEG-2, which is applied to currently used DVD recorders.
The variable bit rate coding method allocates bits to a video signal in response to the characteristic of the video signal (that is, it varies the bit rate) and, thus, it is important to control the bit rate. A representative method of controlling the bit rate is the TM5 algorithm used in MPEG-2. Different bit rates have to be allocated to an intra-coded picture frame (I-frame), a predictive-coded picture frame (P-frame), and a bidirectionally predictive-coded picture frame (B-frame) based on picture type in order to control the bit rate. However, a fixed bit rate is allocated to the I-, P-, and B-frames, and thus picture quality of the I-, P-, and B-frames may deteriorate. Accordingly, it is necessary to control the allocation of bits to the I-, P-, and B-frames in response to the type of input image in order to minimize variation in the picture quality based upon the type of image frame.